The present invention relates to a thin film magnetic head using a magneto resistive element as a read element and to a head gimbal assembly having a gimbal on which the thin film magnetic head is mounted. In particular, the invention relates to structures of terminals connected to the magneto resistive element.
Magnetic disk drives have been downsized and increased in capacity in recent years. Small magnetic disk drives using disks having a diameter of about 90 mm (3.5 inches) and a diameter of about 63.5 mm (2.5 inches) have become mainstream. Since a disk speed is relatively slower in the small disk drives, a problem of reduction in read output is detected with an inductive magnetic head in which the read output depends on the disk speed. To the contrary, since the read output does not depend on the disk speed in a magneto resistive head using a magneto resistive element whose resistance changes depending on a change in magnetic field, the magneto resistive head can provide a high read output in the small magnetic disk drives. Since the magneto resistive head contributes to providing the high read output as compared with the inductive magnetic head even when the track is narrowed to increase density, the magneto resistive head is considered as a thin film magnetic head suitable for downsizing and large capacity.
There are three types of magneto resistive heads: an MR (Magneto Resistive) head using an MR element, a GMR (Giant Magneto Resistive) head using a GMR element, and a TMR (Tunneling Magneto Resistive) head using a TMR element. In this specification, the three heads are collectively referred to as an MR head.
Since the resistance change of the MR element caused by a change in magnetic field is detected in the MR head, a structure of the MR head wherein the MR element is exposed to a slider surface (hereinafter referred to as “air bearing surface”) opposed to a disk provides the highest read efficiency. The exposed type MR head of which the MR element is exposed to the air bearing surface has an MR element edge exposed to the air bearing surface. The exposition of the MR element edge is achieved by polishing part of the MR element during the processing of the air bearing surface. A dimension extending in a direction perpendicular to the air bearing surface of the MR element is called an MR element height, which is controlled by the polishing. Since the read output of the MR head changes depending on the MR element height, the read output is undesirably fluctuated when the MR element heights are varied. Therefore, in order to suppress the read output fluctuation of the MR head, it is necessary to control the MR element heights highly accurately in the polishing.
Since the sensitivity is increased with a reduction in MR element height, the height is getting shorter and shorter yearly. At present, the MR element height is from 0.1 to 0.4 mm and will be reduced to less than 0.1 mm for a thin film magnetic head to be mounted on a magnetic disk drive having a surface recording density of 100 Gbit/in2 or more. Accordingly, a demanded level for the processing accuracy of the MR element height tends to be increased year by year. In addition, it is considered that the processing accuracy demanded for the thin film magnetic head to be mounted on the magnetic disk drive with the surface recording density of 100 Gbit/in2 or more will be ±0.02 mm or less.
In general, the MR element heights are controlled by polishing in such a manner that resistances of a pattern for measurement (hereinafter referred to as “resistance detection elements”) which is formed separately from the MR elements during an element formation process are measured. Then the measured resistances are converted into MR element heights so as to monitor and control the MR element heights during the polishing. For the control method for the MR element heights in a row bar, the MR element heights obtained by converting the resistances of the resistance detection elements formed on several tens of positions in a row bar are approximated by a quadratic curve or a quartic curve, and then a load to be applied on the row bar is controlled during the polishing so as to keep a slope component, a quadratic curve component, and a waviness component of the approximation curve as small as possible.
Further, a thin film magnetic head manufacturing process generally includes two processes for polishing the air bearing surface, i.e., the element height controlling and polishing process for mainly controlling the MR element heights and a bar touch lapping process for reducing a flatness, a surface coarseness, and residual steps of the air bearing surface. A representative method of the bar touch lapping process is disclosed in Japanese Patent Laid-open No. 05-298646 wherein a row bar is brought into close contact with a polishing stool by adhering the row bar to a jig via an adhesive elastic body so that a shape of the stool is transferred to an air bearing surface.
In order to process the MR element heights with increased accuracy, it is considered effective to control a polishing load based on the resistances of the resistance detection elements obtained by in-process monitoring the resistances in the bar touch lapping process. In this case, it is possible to in-process monitor the resistances of the resistance detection elements during the polishing by connecting the resistance detection elements to a measurement circuit of a polisher employing wire bonding as disclosed in Japanese Patent Laid-open No. 2001-101634.